1. Technical Field
The present disclosure relates to a defect inspection apparatus for inspecting a sheet-like inspection object, a computer-implemented method for inspecting a sheet-like inspection object, and a defect inspection system for inspecting a sheet-like inspection object.
2. Description of the Related Art
In the related art, a sheet-like inspection object such as a sheet of paper or a plastic (hereinafter, referred to as a “web”) is conveyed at high speed, where the sheet-like inspection object is normally wound on a roller, for example. The sheet-like inspection object is then irradiated with light and photographed by a camera, and the sheet-like inspection object is inspected for at least one of a surface shape of the sheet-like inspection object and surface defect such as a stipe, unevenness, and foreign matter.
An apparatus that irradiates a web with illumination light to make a shadow on the web, photographs a regularly reflected image or an irregularly reflected image in the shadow using a camera in a dark field sensitivity region, and carries out image processing on an image signal that represents the photographed image to detect defect is known as one example of a method for inspecting a web to determine whether the web has foreign matter defect.
For example, Japanese Unexamined Patent Application Publication No. H8-145907 discloses an algorithm and a defect inspection apparatus capable of comprehensively determining a type of detected defect, for detecting various types of defect in the defect inspection apparatus.
When the above-mentioned defect inspection apparatus is to detect damage on a web, for example, the defect inspection apparatus uses a longitudinal Sobel filter and a lateral Sobel filter, integrates respective pixel values, and detects defect. When the defect inspection apparatus is to detect unevenness, the defect inspection apparatus divides density information into grids each of which has a pixel matrix of a predetermined number of pixels by a predetermined number of pixels, adds respective pixels of density information together within each grid, acquires lateral and longitudinal density variations between the respective grids, and determines that unevenness occurs if the acquired lateral and longitudinal density variations are greater than predetermined amounts.
The above-mentioned defect inspection apparatus is capable of detecting a plurality of types of defect in the single defect inspection apparatus. However, the defect inspection apparatus uses separate algorithms for detecting respective types of defect such as a stripe, unevenness, and a foreign matter. Therefore, reduction in algorithms concerning program processing (i.e., improvement in the speed of inspecting defect) may be possible, and a lot of inspection processing time may be required.